WordNet (r) 3.0 (2006):

pipe up
    v 1: begin to play or sing
    2: utter a shrill cry [syn: shriek, shrill, pipe up,
       pipe]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "pipe up":
   bellow out, blast, blow, blow a hurricane, blow great guns,
   blow over, blow up, bluster, break into music, break silence,
   breeze, breeze up, brew, burst into song, call out, clamor,
   come up, cry out, freshen, gather, holler out, huff,
   make an outcry, make an uproar, outcry, puff, rage, raise a clamor,
   say out, set in, shout out, sing out, speak out, speak up, squall,
   storm, strike up, take the floor, vociferate, waft, whiff, whiffle,
   yell out, yerk out